This invention relates to a mechanical handling apparatus and in particular to a movable arm arranged to be connected to a handling device such as a gripper, vacuum cup or electro magnetic pad.
In present day assembly line manufacture there is a need for routine functions to be performed by a mechanical handling apparatus, usually known colloquially as a "robot". Probably the simplest form of handling apparatus moves in a single plane and has a handling device connected to one end of a movable arm. Such a movable arm may comprise a movable piston mounted in a static cylinder with pneumatic pressure determining the direction and extent of travel of the movable arm. It will be realised that an apparatus capable of moving in two planes can be manufactured by connecting the first arm to a perpendicularly disposed further arm so that, for example, if the first arm moved in a horizontal or x direction then the second arm is made to move in a vertical or y direction. So as to provide a machine capable of moving in a third direction, the z direction, yet a further movable arm similar to the first two arms is connected via a rack and pinion to the second movable arm so that linear motion of the piston is converted to rotational motion to rotate the second, vertically disposed arm. The arms are linked to a programming source in which a series of instructions concerning the movements of the arms is held and in dependence upon the instructions held by the programming source so the arms are able to perform repetitive motions.
In a known mechanical handling apparatus the speed of motion of the arms is slow since it will be realised that the arms must cease movement at a precise point and if the velocity of the arms is too great, overshoot will occur.
The present invention seeks to provide a mechanical handling apparatus which is relatively fast in moving from one point to another and yet which has a high degree of positional accuracy.
According to this invention there is provided a mechanical handling apparatus for point to point movement including arm means connected to a utilisation means, actuator means for driving said utilising means toward a predetermined, prescribed, point, brake means arranged to selectively arrest motion of the arm means and to be driven by a stepper motor means over a predetermined, limited range, and position detecting means arranged to detect the respective positions of the utilisation means and of the brake means relative to a datum, the position detecting means being connected to a control means and said control means defining the point to point movement instructions of the utilisation means and being arranged to sequentially energise the actuator means, if required, to drive the utilisation means towards said prescribed point and within the range of said stepper motor means, activate the brake means to arrest motion of the arm means and drive the stepper motor means to bring the utilisation means to the prescribed point.
The apparatus at the present invention enables the utilisation means to be rapidly driven to approximate desired stopping point by the actuator and then to be accurately located by the stepper motor means so that the advantages of high speed and good accuracy are obtained.
Preferably, the actuator means comprises a cylinder and associated movable piston, said piston being connected to the arm means, a pressure source and a valve means arranged to maintain the piston substantially in force balance by application of force from said pressure source until activated by a signal from the control means.
Advantageously the arm means comprises a load beam means connected to and movable with said piston, said load beam means being supported by bearing means.
Normally the control means includes a store means containing said point to point movement instructions and coordinates.
Preferably, the pressure source is a source of compressed air, the actuator means is pneumatic and the valve means comprises at least one electrical solenoid operated air valve connected between the pressure source and a respective side of the piston in the cylinder with a regulator in one of the lines to ensure a different pressure on opposing sides of the piston and thereby maintain the piston in substantial force balance until activated to destroy the force balance.
Conveniently the air valves of the valve means have a normally open port connected to the pressure source, a common port connected to a respective side of the piston and a normally closed port connected through the intermediary of a piston velocity governing means to an exhaust.
Preferably the pressure source is also connected to the normally closed port of an air valve determining the operation of the brake means. In a preferred embodiment the piston velocity governing means comprises a plurality of electrical solenoid operated air valves connected such that any one or combination thereof vents air from said valve means in an amount determined by the position of the piston in the cylinder whereby the piston is driven with a substantially constant, predetermined, velocity irrespective of the position thereof within the cylinder. Advantageously, the vent ports of respective valves of the piston velocity governing means have differing cross-sectional areas to maximise the number of different vent cross-sectional openings and in such manner provide said substantially constant predetermined velocity of the piston.
Advantageously the load beam means comprise a load beam having on respective opposing sides thereof a rail, each rail being arranged to be guided by said bearing means which comprise a pair of longitudinally disposed rollers for each rail. The load beam conveniently has an inverted U shaped cross section.
Preferably the brake means comprises a calliper having two arms which are pivoted at one end and carry friction material at the outer faces of the free ends thereof for engagement with the inside faces of the U shaped load beam in dependence upon the position of an activating means. Conveniently the activating means comprises a cylinder formed in the outer surfaces of each arm intermediate the pivot and friction material, a dumb bell shaped piston extending across the pivot axis of the calliper with a pressure equalising channel extending through the central portion of the dumb bell into each cylinder, a port for admitting pneumatic pressure to one of the cylinders and a compression spring for maintaining the non-activated state of the brake means, whereby in operation the piston is stationary and the callipers move. In the currently preferred embodiment the brake means is normally held in engagement with the load beam means and is released by admitting pneumatic pressure to one of the cylinders.
Preferably the stepper motor means is connected to a lead screw upon which the brake means is located in a substantially backlash free manner, the axis of the lead screw being substantially parallel to the axis of the load beam means. Advantageously, the brake means is mounted on the lead screw through the intermediary of axially disposed recirculating ball nuts. So as to permit a small amount of axial misplacement a flexible coupling is provided between the stepper motor means and the lead screw.
The position detecting means is advantageously an absolute displacement transducer known as a Temposonic series DCTM comprising a rod having at one end thereof means for producing an electrical launch pulse at a predetermined repetition rate and a torsion transducer, and circumferentially surrounding said rod and longitudinally spaced therealong is a pair of magnet means, one connected to travel with the load beam means and the other connected to travel with the brake means, and distance determining means for determining the time taken for a launched pulse to be returned from a respective one of the magnet means as a torsion pulse to the torsional transducer from which time the position of the respective magnet means can be determined. Normally the magnet means is formed by four equi-circumferentially spaced magnets.
Preferably the control means further includes an electronic microprocessor connected to receive and provide inputs to the store means and the position detecting means, and in dependence thereon to transmit commands to the valve means, the piston velocity governing means, the valve determining the operation of the brake means and the stepper motor means.
Conveniently said store means comprises a CMOS random access memory (CMOS RAM) for data storage and a random access memory (RAM) for temporary data storage. Advantageously the CMOS RAM is arranged so that after each terminal point of travel of the utilisation member has been reached it updates the information in the RAM so that a minimum amount of travel of the brake means along the stepper motor lead screw is required.
The utilisation means may be pneumatic finger members, vacuum cups or electro magnetic pads.
Preferably motion in x and y perpendicularly disposed directions is provided by mounting two arms perpendicularly arranged with respect to each other such that the utilisation means of one is the arm of the other. For motion in three mutually perpendicular x, y and z directions the utilisation means of each of two arms are connected in mutually perpendicular fashion to a different arm such that the mounting for the x arm forms the apparatus mounting respective to which motion takes place in each of the three directions.
Advantageously the store means contains information concerning spatial parameters defining a no-go area through which it is impermissible for the utilisation means to pass and instructions are provided to enable the utilisation means to manoeuvre around such a no-go area.
Conveniently, the store means is provided with a plurality of differing sets of strategy information, each set defining a type of motion the utilisation means is to make, and means are provided for selecting a particular strategy in combination with start and finish co-ordinates the utilisation means is to adopt, whereby the motion of the utilisation means between its start and finish coordinates is determined by the strategy selected.